A printed circuit board (PCB) is a composite structure comprising one or more dielectric material layers having a metal (e.g. copper) laminate bonded thereto. The metal laminate is patterned, forming conductive traces or transmission lines for carrying electrical signals, for example, between components arranged on the PCB. Multilayer PCBs are realized when two or more layers of dielectric material having patterned metal bonded thereto are laminated together under heat and pressure. Electrical interconnections made through layers of the PCB are typically achieved using metal-plated holes, or vias. Smaller “micro vias”, which are typically of a blind nature (i.e. do not pass completely through the PCB stack), are also commonly used to increase PCB component density. Ground and power planes are provided for distributing voltages to the circuit components arranged on the PCB.
The desire for increased PCB density and higher-power applications have led to several technical challenges. Such challenges include decreasing the excess interference or crosstalk between closely-located components and their associated electrical interconnections. This interference is dependent upon, for example, proximity of the electrical interconnections, signal power levels and frequency rates. In many modern high-frequency applications, including radio frequency (RF) applications, the degree of isolation between and among conductors and other circuit features, such as vias, needs to exceed 40 dB.
In addition to creating layer-to-layer electrical interconnections, metalized vias may also be used to isolate components of PCBs. These ground vias may be arranged in several different patterns, such as uniform rows, double rows and the like for providing isolation, for example, between adjacent transmission lines and other features. A drawback of these ground “via fences” is that these arrangements occupy valuable space on the PCB, limiting the extent to which the spacing or pitch between electrical interconnections may be reduced to increase PCB density. For example, RF transmission lines and layer-to-layer transitions require ground via spacing of λ/10, of the highest operating frequency, on both sides of the feature to create ground continuity and mitigate undesirable resonances and excited modes from the signal.
Alternative systems and methods for providing isolation between PCB features are desired.